Thread break detection device



Dec. 1, 1964 Filed 000. 20, 1961 H. A. GODWIN ETAL THREAD BREAK DETECTION DEVICE 2 Sheets-Sheet 1 FIG.

FIG. 5

- INVENTORS Dec. 1, 1964 H. A. GODWIN ETAL THREAD BREAK DETECTION DEVICE Filed (Jo t. 20, 1961 2 Sheets-Sheet 2 3,159,123 THREAD BREAK DETECTIGN DEVICE Homer A. Godwin, Wellsburg, Frank G. Brockardt, Wheeling, and Joseph'tll. Koch, Elm Grove, W. Va, assignors to West Virginia Pulp and Paper Qompany,

New York, N.Y., a corporation or Delaware Filed Oct. 20, 1961, Ser. No. 146,539

4 Claims. (Cl. 112--219) This invention relates to a control mechanism for sewing machines and more particularly to a simplified, gravity actuated device that automatically stops the machine when a thread break occurs or thread terminates.

Thread break devices are necessary on modern, highspeed sewing machines, for a large quantity of material would pass through the sewing machine and be damaged before a thread break was visually detected by the machine operator and the machine stopped.

In the past many complex devices have been devised for detecting thread breaks and stopping sewing machines upon a break. However, the complexity of some of these devices has proved unsuitable for factory operations where adverse conditions, such as vibration, dust and dirt, may exist. Some of the devices in the prior art have utilized a shutter system in conjunction with a beam of light to detect thread breaks, others have utilized springloaded or electromagnetic switches of various types to detect the breaking of a thread, but none have disclosed the simplified gravity actuated device developed by this invention wherein an open circuit switching element is utilized. It has been discovered that normally closed switches that are small and sensitive do not hold a completely closed circuit under normal vibration present when mounted on an operating sewing head. Under actual sewing conditions the contacts scrub each other but do not open completely. This scrubbing together of the contacts causes a small leakage sufficient to open the control circuit of the sewing machine. This invention maintains normally open contacts completely eliminating the problem of scrubbing caused by vibration. By mounting the microswitches used in the detector on the sewing machinehead and the motor control circuit relay at a point away from the vibration area such as the machine frame, difliculties in the detection circuit caused by vibration are eliminated.

. in the drawings:

FIG. 1 is a front view showing a sewing machine head with a thread break detection device attached on each thread line.

FIG. 2 is a front view of the thread break detection device with the thread in running position and the microswitch in open position.

FIG. 3 is a cross-sectional view of FIG. 2 taken along line 3-3.

FIG. 4 is a fragmentary front view of the thread break detection device showing the thread line broken and the microswitch in the closed position.

FIG. 5 is a circuit diagram showing the two microswitches wired in parallel and in open position with the motor circuit closed.

In FIG. 1 a sewing machine head it) is shown with two of the thread break devices12 and 14 attached. It is to be understood that any number of devices may be used consistent with the number of threads being used; In

most sewing machines only two thread lines are utilized and a break detection device is used on each line to shut off the machine if a thread break occurs in either thread line. When more than one device is used, they are wired in parallel into the relay circuit.

The thread break detector housing 16 is mounted on sewing machine head by means of bolts 18 and 20. The housing 16 contains the thread break detection ele- United States Patent 0 3,159,123 Patented Dec. 1, 1964 ments and also provides a means for easily attaching the housing to the sewing machine head. Though the housing 16 shown in FIG. 1 is made to accommodate two detector units, it is readily seen that the lower part of the housing forms a complete single unit if only one thread line is used. The housing may be of any shape to suitably encase the detection elements. Housing 16 may be cast of aluminum or any other suitable material. A plexiglas cover 17 may be placed over the part of the housing 16 containing the detection elements to keep out dust and dirt. As shown in FIG. 3 the housing 16 is provided with an internal ledge 22 which has a hole to allow the cylindrical vertically movable thread support member 24 to move vertically through the ledge. Thread support member 24 has an eye at its bottom and through which the thread line passes. The movement of the vertically movable thread support member 24 is controlled by upper stop 26, a cylindrical metal body which moves freely on member 24 and which may be adjusted with a set screw to give the vertically movable thread member 24 a predetermined amount of downward travel. Lower stop 23, which is of similar construction to stop 26, is placed below the internal ledge 22 on member 24 so that when a thread break occurs and member 24 moves downward, lower stop 28 carries coacting lever arm'3i downward to close the open microswitch 32 which is a simple single pole single throw switch to which lever arm 30 is pivotally attached. Any other suitable sensitive switch which is enclosed may be used in place of the microswitch.

The lever arm 30 closes open microswitch 32- and a relay 34 of convention single pole, single throw construction is actuated which opens the motor circuit 36 and stops the motor 37 which operates the sewingmachine. Relay 34 is normally closed until it is opened by a closed microswitch. This may be more clearly seen in the circuit diagram shown in FIG. 5 where in normal operation the microswitch 32 is open and the motor circuit 36 closed. The relay 34 is preferably mounted away from the machine to be free from vibration. When a thread break occurs the microswitch 32 closes the relay circuit which actuates relay 34, which in turn opens the motor circuit 36, thus shutting off the motor which operates the sewing machine. When the thread line is repaired and the vertically movable member 24 is then held in its up position by the thread line as shown in FIG. 2, microswitch 32 is opened and the relay 34 returns to its normally closed position, thus closing motor circuit 36 and the sewing machine is again ready to operate.

The fragmentary view of FIG. 4 shows the working mechanism of the thread break device when a thread break occurs. The thread line 38 passing through stationary guides 40 and 42 falls away from the guides allowing gravity to move vertically movable thread guide memer 24 downward a predetermined distance as limited by upper stop 26, thus closing microswitch 32, opening relay 34, and breaking motor circuit 36. Applicants construction provides for an extremely lightweight vertically movable thread guide member which exerts a thread load of only approximately 113 grains or ounce. It will further be noted that while the sewing machine is running and thread is passing through the detection device the micr-oswitch 32 is in an open position; thus it is not affected by vibration of the sewing machine head as would be a device utilizing a closed switch type arrangement. The lightweght of the vertically moving member provides little friction to hinder the movement of lever 39 pivotally connected to microswitch 32. The actuation of the microswitch 32 by the downward movement of the vertically movable thread guide member being caused by gravity alone completely eliminates the necessity of electromagnetic or spring means to actuate the microswitch, thus 3 providing a simple device of low initial cost that may be easily maintained during production use in the factory.

Many other advantages of the device of this invention will be apparent to those skilled in the art and other obvious embodiments within the skill of the art are intended to be included in the following claims.

We claim:

1. A thread break detection'device for a sewing machine comprising a housing, said housing suitable for mounting on a sewing machine, stationary thread guide means attached to the bottom of said housing, a vertically movable elongated thread guide member extending through the bottom of said housing, a lower stop attached to the vertically movable thread guide member, an electrical switch attached within said housing, a lever arm pivotally attached to said electrical switch and coacting with the tower stop to close the electrical switch when the vertically movable member has moved downward a predetermined distance.

2. A thread break detection device for activating a relay to open the motor circuit of a sewing machine comprising:

(a) a housing suitable for mounting on a sewing machine, said housing having an internal ledge, said in ternal ledge having an aperture;

(b) stationary thread guide means attached to the bottom of said housing;

(0) a vertically movable thread guide member extending through said aperture and through the bottom of said housing;

(d) an upper stop attached to the vertically movable thread guide member;

(e) a lower stop attached to the vertically movable thread guide member;

(f) .a microswitch attached within said housing;

(g) a lever arm pivotably attached to said microswitch and coacting with said lower stop to close said microswitch when the vertically movable thread guide member has moved downward to a predetermined position; and

(h) a relay electrically connected to said microswitch, the microswitch, when closed, activating said relay to open the motor circuit of the sewing machine.

3. Apparatus according to claim 2 wherein t l e upper step has means for adjustably mountin the stop on said vertically movable thread guide member.

4. Apparatus according to claim' 2 wherein the lower stop has means for adjustably mountingthe stop on said vertically movable thread guide member.

References Cited in the tile of this patent UNITED STATES PATENTS 1,545,692 Planeuf July 14, 1925 2,643,306 Hamilton June 23, 1953 2,651,275 Moore Sept. 8, 1953 2,938,972 Bryson May 31, 1960 3,021,401 Young Feb. 13, 1962 

1. A THREAD BREAK DETECTION DEVICE FOR A SEWING MACHINE COMPRISING A HOUSING, SAID HOUSING SUITABLE FOR MOUNTING ON A SEWING MACHINE, STATIONARY THREAD GUIDE MEANS ATTACHED TO THE BOTTOM OF SAID HOUSING, A VERTICALLY MOVABLE ELONGATED THREAD GUIDE MEMBER EXTENDING THROUGH THE BOTTOM OF SAID HOUSING, A LOWER STOP ATTACHED TO THE VERTICALLY MOVABLE THREAD GUIDE MEMBER, AN ELECTRICAL SWITCH ATTACHED WITHIN SAID HOUSING, A LEVER ARM PIVOTALLY ATTACHED TO SAID ELECTRICAL SWITCH AND COACTING WITH THE LOWER STOP TO CLOSE THE ELECTRICAL SWITCH WHEN THE VERTICALLY MOVABLE MEMBER HAS MOVED DOWNWARD A PREDETERMINED DISTANCE. 